Histopathology of the conduction system in sudden death from coronary heart disease.

Sudden cardiac death (SCD) has been attributed to the development of lethal dysrhythmias in coronary heart disease victims, and several recent autopsy surveys showed that 10 to 50% of SCD patients had unsuspected acute myocardial infarction (AMI). The present study concerned histopathological findings of the conduction system in 49 SCD (within six hours of the onset of acute symptoms) patients; 39 with established AMI (group A) and ten without (group B). Both groups showed high incidence of cardiomegaly, significant coronary artery disease affecting one or more vessels, and acute myocardial ischemia detectable by specific histological criteria. Stenosis of nutrient vessels of the conduction system was present in about 50% of the atrioventricular (A-V) node arteries and about 25% of the sinoatrial (SA) node arteries in both groups of SCD patients. Nonspecific "degenerative" changes (fibrosis, fatty infiltration, or both) of the conduction tissue, which might or might not represent results of old ischemic injury, also occurred with similar frequencies. Acute changes (infarction, hemorrhage) of the A-V node and bundle branches were found only in two group A patients, both had massive septal infarction. Thus, the conduction tissue appeared more resistant to ischemic injury and was overtly damaged only on rare occasions in fatal AMI. The scarcity of acute lesions in the conduction system itself suggested that lethal dysrhythmia in SCD was probably due to electrical instability of the acutely ischemic contractile myocardium rather than a direct injury to the specialized tissue of the heart.